This invention relates to a pneumatic fastener driving device and, more particularly, to such a device having an improved nose sealing arrangement.
Conventional pneumatic fastening devices of the type contemplated herein include a valve arrangement moveable in response to actuation of a trigger from a closed position to an open position permitting air under pressure to communicate with a piston chamber for moving a piston and fastener driving element fixed thereto through a cylinder, thereby initiating a fastener drive stroke. The valve arrangement permits a single driving stroke upon actuation of the trigger, or automated cycling of the fastener device for repetitious operation. Fastener devices of the single drive stroke type can be standard, wherein the fastener driving element is moved to the bottom of its stroke upon actuation of the trigger, and to the top of its stroke upon release of the trigger. Alternatively, devices of the single drive stroke type can be of the full cycle type, wherein a drive stroke and return stroke of the fastener driving element occurs upon actuation of the trigger, and returns to the top of its stroke upon release of the trigger. In the automated fastening device type, a plurality of fastener drive strokes and return strokes are accomplished so long as the trigger continues to be actuated.
In any of these devices, the piston and fastener drive element is driven downwardly in a drive stroke by air pressure within the cylinder above the piston, and initiates a return stroke to the top of the cylinder upon pressurization of the cylinder below the piston.
To provide for an efficient return stroke, it is important for the space within the cylinder below the piston to be sealed as efficiently as possible to permit the build-up of air pressure required for maximized piston return responsiveness.
In a known arrangement for sealing the lower chamber, as set forth in U.S. Pat. No. 5,511,714, a mouth tool is provided with an extension portion which is forced into sealing relation within a recess provided in a stop member at the bottom of the drive cylinder. The stop member is formed from a block of resilient material confined by the drive cylinder. The seal between the mouth tool and the stop member is formed as a result of pure mechanical compression of the resilient material and the resultant inwardly biased force it applies to the mouth tool inserted into the recess. A problem with this arrangement is that when the lower cylinder is pressurized to move the drive piston upwardly during a return stroke, the pressure within the lower part of the cylinder operates to bias or flex the resilient stop member away from its sealing engagement with the mouth tool. It can be appreciated that after prolonged use of such tool under pressure and impact conditions, the seal between the mouth tool and the stop member may be compromised. Furthermore, the tolerances of the stop member and the mouth tool must be made sufficiently small at the sealing interface therebetween to enable the mouth tool to be properly sealed to the stop member while also permitting the mouth tool to be easily inserted in sealing relation with the stop member. More specifically, if the recess in the stop member is too large, it will not properly seal with the mouth tool. On the other hand, if the recess is too small, it becomes difficult to insert the mouth tool. It is, therefore, an object of the invention to provide a pneumatically operated fastener drive device that overcomes the problems noted above.
In accordance with this object, the present invention provides a pneumatically operated fastener drive device that comprises a housing assembly including a nose assembly defining a fastener drive track. A cylinder is disposed in the housing assembly, and a resilient bumper is disposed towards a bottom of the cylinder. A drive piston is slidably and sealingly mounted in the cylinder for movement through an operative cycle including a drive stroke and a return stroke. The drive piston engages the bumper at the end of the drive stroke. A fastener driving element is operatively connected to the piston. The fastener driving element extends through an opening in the bumper and is movable in the fastener drive track through a drive stroke in response to the drive stroke of the piston and a return stroke in response to the return stroke of the piston. A valve arrangement includes a normally closed main valve which is movable from its closed position to an opened position to allow air under pressure to communicate with an area within the cylinder above the piston to initiate and effect movement of the piston and fastener driving element through the fastener drive strokes thereof. An actuator and trigger member are operable to control the valve arrangement. The bumper has a sealing portion surrounding the opening in the bumper and disposed outwardly from the cylinder. The sealing portion has exterior surfaces disposed in engagement with adjacent surrounding surfaces of the nose assembly. The sealing portion being flexible outwardly under the force of air pressure within the cylinder below the piston during the return stroke of the piston so that the exterior surfaces of the sealing portion are biased in sealing relation with adjacent surrounding surfaces of the nose assembly.
Other objects and advantages of the present invention will become apparent from the following detailed description and drawings and appended claims.